A method for attaching a vibration- or shock-sensitive device, such as a stereo system, compact disc player, CD changer, or floppy or hard disk drive to a supporting member and mounting the supporting member with vibration damping in a housing via helical spring elements is already known. Particularly in motor vehicles, low-vibration and low-impact methods of attaching compact disc players are required in order to operate the equipment without interference. For this purpose, the device is thus elastically suspended on the equipment housing, which is permanently installed in the motor vehicle, with the supporting member being attached to the housing via multiple helical spring elements provided in the form of either extension springs or compression springs.
FIG. 1a shows a conventional spring arrangement using extension springs, and FIG. 1b shows the arrangement using compression springs. In FIG. 1a, a supporting member 2 in the form of a plate, with a compact disc player 1, for example, attached to its top, is fastened to the top of a cuboid housing 3 via a total of four helical springs (10, 11), only two of which are illustrated. According to this arrangement, an excitation acting upon housing 3 produces only an extremely diminished acceleration of CD player 1. By suspending the device in this manner, points of resonance form which are associated with an undesirable, strong vibration of device 1 at low excitation frequencies, thus causing device 1 to bump against housing 3. To avoid this disadvantage, it is desirable to increase natural frequency wmax of the system subject to vibrations, since this will considerably diminish the acceleration of CD player 1 during excitation. With a given mass M according to equation (1), this can be achieved only by increasing spring constant K.                               ω          max                =                              K            M                                              (        1        )            
However, the supporting plate suspended on springs 10, 11 in FIG. 1a must be displaced by the force of its own weight until it ends up more or less in the center of the vibration clearance provided for it, the height of which is marked x in FIG. 1a. This can be achieved by reducing the spring constant, which, however, should be avoided as shown by equation (1), due to the resulting undesired reduction in the natural frequency. The spring arrangements illustrated in FIG. 1a and FIG. 1b also have the disadvantage that they can be used only in situations where the springs are loaded axially, i.e., in the direction of the spring axis. However, the springs are more compliant when the force is applied radially. The springs are barely extended in that case, but rather are merely swivelled or bent. As a result, only weak restoring forces are applied in the radial direction. Radially oriented forces act upon the springs when the device is installed in the motor vehicle in a direction other than the specified mounting position. A situation of this type is illustrated in FIG. 2a. When device 3 tilts to the side, supporting member 2 is displaced far to the side by its weight, thus reducing the vibration clearance. If a vibration or impact excitation occurs, there is the danger of the device striking the side walls of the housing. The use of a spring arrangement, like the one shown in FIG. 1, is therefore limited to situations in which the compact disc player is specifically designed for a predetermined mounting position, e.g., if it can be installed in the vehicle only horizontally or only vertically. Compact disc players in car radio equipment often need to be installed in consoles at an angle. If the player housing is attached to the roof structure of a bus, for example, a certain angle of inclination is desirable in order to make the CDs easier to insert. According to the related art, supporting member 2 is attached to housing 3 in such situations, using an additional spring 19 that is adjusted to the angle of inclination. This also has the disadvantage that the CD player can be installed in no position in the vehicle other than the predetermined one. That is why some devices include an adapter mechanism which can be used, for example, to adjust a CD changer to the mounting position at hand within certain limits. The known related art is illustrated in FIG. 7a and FIG. 7b. FIG. 7a shows the device with its housing 3, initially mounted in a horizontal position. The CD changer (not illustrated) is attached to a supporting member 2 that is suspended on two discs 40 via two springs 10 and 11 so that supporting member 2 is located more or less in the center of the vibration clearance provided for it. Discs 40 are each attached to the side walls of device housing 3 so that they can rotate around an axis 41. If the device is installed in a horizontal position, springs 10 and 11 are located in position A in FIG. 7b. If the same device is now installed in a vertical position in the motor vehicle, housing 3 is first rotated 90 degrees, and the two discs 40 are rotated 90 degrees in the opposite direction on actuating element 42 until springs 10 and 11 are in position B shown in FIG. 7b and subsequently locked in place. The elastic force of springs 10 and 11 compensates for the weight of supporting member 2, along with the device arranged upon it, so that the supporting member can also vibrate freely in the housing even when mounted in a vertical position. Any intermediate positions between 0 and 90 degrees can also be set. The disadvantage of this related art is that it requires an expensive adapter mechanism, which increases the device production costs. A relatively complicated adjustment of the adapter mechanism to the different mounting positions is also necessary, making it possible to incline the device only around an axis that runs parallel to axes 41.
The spring arrangement according to the present invention has the advantage that both the spring constants of the individual springs and the natural frequency of the system can be increased. This is achieved by mounting the supporting member in a predetermined position in the housing. A component of elastic force applied in a specific direction is then always counteracted by a component of elastic force in the opposite direction. This prevents the springs from lifting or lowering the supporting member too far away from the center of the preset vibration clearance when using very rigid extension springs or compression springs. At the same time, the supporting member can be installed in different positions in a motor vehicle without having to adjust the spring arrangement or use an adapter mechanism. Another advantage is that the position of the supporting member relative to the housing varies only slightly in different mounting positions, allowing the device to be operated without interference independently of the mounting position when vibrations or shocks occur.
This is essentially achieved by the fact that the springs not only swivel or bend when the housing tilts or rotates, as in the case of the related art illustrated in FIG. 2a, but rather that, with the spring arrangement according to the present invention, the supporting member is mounted in such a way in the housing that the springs are extended when the supporting member is displaced in any direction. As a result, restoring forces always counteract the displacement.
For example, the spring arrangement is advantageously designed so that the supporting member is arranged more or less in the center of the vibration clearance. This prevents the device from bumping against the housing at high oscillation amplitudes.
A further advantage is the use of inexpensive extension springs, the ends of which can be easily attached to the supporting member and housing and then released again, since this reduces the amount of installation work needed, making it cost-effective.
A further advantage is to design the supporting member in the form of a flat, rectangular supporting plate. The rectangular supporting plate can be advantageously mounted in a cuboid housing using springs provided in the corner areas.
A further advantage is provided by mounting the supporting plate in the housing using four extension springs projecting from the plate top and bottom, since this provides stable, elastic mounting of the supporting plate in the center of the vibration clearance and parallel to the upper and lower housing walls.
If the supporting plate is attached to the upper housing wall by two extension springs in two diagonally facing corner areas of its top and to the lower housing wall by two springs projecting from its bottom, four springs are sufficient in order to mount the supporting plate elastically in the housing. This can reduce the production costs.
A particular advantage is provided by mounting the supporting plate in the housing with extension springs projecting at an angle from the plate and facing away from it. This allows the springs to extend even farther, with the resulting restoring forces being even stronger, when the device is mounted in an inclined position.
If the supporting plate is attached to the housing by extension springs that are fastened to the longitudinal sides of the supporting plate and oriented more or less parallel to it, an arrangement with three springs positioned on same plane as the supporting plate is sufficient.
In some situations, e.g., in the case of a CD changer, the vibration-sensitive device is attached to a cuboid supporting member. In such situations, the cuboid supporting member is advantageously suspended between two opposite side walls of the housing using two tapered springs. The first and last coils of the tapered spring do not contribute to spring compliance and are advantageously firmly attached to the side walls in an attachment area lying flat against the side walls. The tapered springs allow the supporting member to be mounted in the housing in a manner that is particularly space-saving and economical.